The present invention relates to a portable electronic apparatus such as an integrated circuit (IC) card which may be used as a credit card in conjunction with a shopping system, for example.
Recently, an IC card incorporating an IC chip containing an erasable non-volatile memory and a central processing unit (CPU) controlling this memory has been developed as a new portable data memory medium. The IC card allows a variety of data to be input and output in conjunction with external sources by means of the internal CPU which accesses the memory.
Conventionally, the IC card is used in a shopping system in a similar manner as a credit card. The limit of the total amount of charges that may be applied to the card in a month (credit limit) is stored in the IC card. When making a purchase, an operator inserts the IC card into terminal equipment and inputs the charge amount by operating a keyboard of the terminal equipment. The terminal equipment generates a new credit limit by subtracting the input amount of the transaction from the credit limit stored in the memory of the IC card and stores the new credit limit in the memory.
The credit limit stored in the memory of the IC card is renewed every predetermined term, for example the first day of each month. Conventionally, the credit limit is renewed by using the IC card with specific terminal equipment owned by the IC-card issuer. In other words, while using any conventional IC card for purchasing merchandise on credit, only the IC-card issuer can renew the credit limit. As a result, each IC-card holder must seek out an appropriate terminal for renewing his credit limit to continue transactions each term. This is bothersome and inconvenient to all those who hold IC cards.
As an alternative, a study is underway to explore the possibility of renewing the credit limit by means of on-line communication with a host computer. Nevertheless, if this idea is adopted, all IC card holders will be obliged to communicate with the host computer via terminal equipment whenever renewing the credit limit, thus incurring a heavy burden to them in bearing the cost of on-line communication facilities and the communication itself.
In addition, recently, a battery-powered IC card has also been developed, which incorporates a battery and is provided with a keyboard and display and operates without being connected to terminal equipment.
European Patent Publication No. 0167044 (published Aug. 1, 1986) discloses an IC card which is provided with a battery, keyboard and display. In addition, this IC card incorporates a clock and identifies the expiration of the card itself, not only to provide a time after which a new card is required (as is conventional) but also to provide a time after which the battery in the card may fail. Nevertheless, this publication does not disclose means for renewing the credit limit for transactions with the IC card.